1. Field of the Invention
The invention relates to a pyrogen, which depends for its heating effect on a metal redox reaction, and a self-heating canister which incorporates said pyrogen and which is used either to cook or simply to heat up various foodstuffs such as grains, noodles and beverages.
2. Description of the Prior Art
A substantial number of proposals have already been made in respect of pyrogens which make use of the exothermic oxidation of metals (for example: Japanese patent publication gazette S27-582, Japanese utility model laying open gazette S58-24119, and Japanese patent laying open gazette S62-17287, S63-51491, and H1-284582). All these proposals have involved the admixture of metal oxides and peroxides to one or more of the powders of iron, aluminum and ferrosilicon.
When a pyrogen which makes use of peroxides in this way burns, however, the peroxides not only react with the Si but also break down through a process of pyrolysis. This results in the freeing of oxygen gas which in turn facilitates the generation of sparks and flames which are sometimes emitted from the container thereby creating an obvious hazard. Another drawback with this type of pyrogen derives from a tendency to swell rapidly following combustion and to assume a sort of spongelike form under the influence of the aforementioned free oxygen gas.
Japanese patent laying open gazette H1-288218, on the other hand, disclosed the use of a pyrogen composed of ferrosilicon powder plus one or both of the substances Fe.sub.2 O.sub.3 and CuO. Since the pyrogen does not in this case contain peroxides, the amount of oxygen gas which is freed is considerably reduced but even so, since it is not, in fact, altogether eliminated, the aforementioned problem of the swelling and deformation of the pyrogen following combustion remains.